Reverse current controlling electrode with oversize backing

ABSTRACT

A medical electrode includes a moderately conductive flexible member having a top side and a bottom side with a connector and contact with a flexible member top side for establishing electrical contact with an external apparatus. An oversize non-conductive flexible sheet covers the conductive flexible member top and the connector and a highly conductive ink pattern is disposed on a conductive flexible member bottom side. A moderately high conductive hydrogel adhesive disposed on the conductive flexible member bottom side and covering the conductive ink pattern is provided for adhering the electrode to a patient&#39;s skin.

The present application is a continuation-in-part of U.S. Ser. No.10/359,988 filed Feb. 6, 2003. This reference patent application is tobe incorporated herein in toto by the specific reference thereto.

The present invention generally relates to electrodes and, moreparticularly, electrodes suitable for transcutaneous nerve and/or musclestimulation and biological signal recording.

Medical electrodes must provide an even electrical distribution to apatient's skin over an entire surface of the electrode to assure propercoupling. Because of the curvaceous nature of the human body, it isapparent that medical electrodes for use thereon must be flexible notonly for confirmation with a patient's skin contours, but also toaccommodate relative movement of the patient's skin.

It is well known that inadequate flexing and shaping of the electrode toa patient's contour can result in an irritation of the patient's skin.Electrical “hot spots” due to uneven electrode-skin contact can resultin a rash or a burning sensation. A sensation of burning may be felt bya patient within a few minutes after application of the electricalsignals during nerve and/or muscle stimulation, while rash conditionsgenerally take a longer period of time to develop.

In order to provide uniform electrical coupling, heretofore developedelectrodes have utilized conductive fabrics and foils in combinationwith a conductive and flexible adhesive in order to uniformly coupleelectrical signals to and/or from an electrical lead wire, or connector.

A number of electrodes have provided impedance compensation fordirecting electrical pulses from the lead wire uniformly throughout anelectrode, such as, for example, U.S. Pat. No. 5,038,796 entitled,ELECTRICAL STIMULATION ELECTRODE WITH IMPEDANCE COMPENSATION, and U.S.Pat. No. 5,904,712 CURRENT CONTROLLING ELECTRODE to Axelgaard. U.S. Pat.No. 4,736,752 teaches the control of current density across an electrodethrough the use of conductive ink design areas. These patents areincorporated in their entirety herewith by this specific referencethereto.

Many prior art electrodes have compromised the flexibility of theelectrode in order to provide adequate current densities over the entirecontact area of the electrode. Such electrodes typically have utilized ametallic mesh, or foil, to provide conductivity and utilize a conductivegel between the electrode and the patient's skin in order to accommodatethe movement therebetween. Such use of foil or mesh often cause burningor hot spots at electrode edges.

The present invention is directed to a medical electrode having acombination of conductive elements, with selected conductivities whichenables assembly of the electrode in a manner hereinbefore not possible.More specifically, the present invention is directed to a medicalelectrode having a connector disposed on a top surface of a conductivemember. This enables automated assembly of the electrode as opposed toconventional manual assembly which in turn reduces unit cost while atthe same time providing for controlled and even current density.

SUMMARY OF THE INVENTION

A medical electrode in accordance with the present invention generallyincludes a moderately conductive flexible member having a top side and abottom side with a highly conductive pattern, such as, for exampleconductive ink, printed or transferred to the member bottom side.

A conductive adhesive of moderately high conductivity is disposed on theflexible member bottom side and covering the conductive pattern foradhering the electrode to a patients' skin.

Importantly, the use of a moderately high conductivity adhesive enablesthe placement of a connector on the top side of the flexible memberwhile at the same time providing uniform current distribution by theelectrode. This arrangement is reverse to the configuration of prior artelectrode such as set forth in U.S. Pat. No. 5,904,712 and accordinglyhas been named “Reverse Current Controlling Electrode”.

In controlling current density, the surface resistivity of theconductive member may be between about 102 and about 106 ohm/cm, theresistivity of the conductive pattern may be between about 0.1 and about10 ohm and the volume resistivity of the adhesive may be between about102 and 104 ohm cm. The conductivity of the conductive pattern can becontrolled through the use of various grid designs with preselected linewidths and spacing as well as thickness and ink compositions.

The connector is disposed over the conductive ink pattern and on the topside of the conductive member, whereas the ink pattern is disposed onthe bottom side of the conductive member. This arrangement enables theconnectors to be disposed in any selected points within a perimeter ofthe pattern without affecting current distribution. This flexibility ofconnector positioning, provided by the present invention, facilitatesmanufacture of the electrodes. In addition, because the lead wire is notdisposed between the conductive pattern and patients' skin, there is nointerference with the electrode current distribution as is the case whenthe lead wire is disposed between the conductive pattern and thepatients' skin as is the case with some prior art electrodes.

A non-conductive flexible sheet may be disposed over the connector onthe conductive flexible member top side. The non-conductive flexiblesheet preferably has dimensions greater than said conductive flexiblemember causing an overlap thereof. This arrangement facilitatesmanufacture and also eliminates the need for precise alignment with theconductive flexible member. It also prevents gel from folding around anedge of the conductive flexible member and attaching itself to clothing,etc.

An adhesive is provided for bonding the non-conductive flexible sheet tothe top side of said conductive flexible member and also for securingsaid connector to said conductive flexible member top side;

In one embodiment of the present invention, the conductive pattern isdisposed on the conductive flexible member bottom at a spaced apartdistance from a perimeter of the conductive flexible member in order toestablish a border between the perimeter of the conductive ink patternand the conductive flexible member perimeter. This is important inproviding controlled “roll off” of electrical current distribution.While even and uniform electrical current density across the electrodeis the desired distribution, such current density should not be presentat the edge of the electrode since it may cause unwanted stimulation atthat site. Thus, it is most desirable to have the current density “rolloff” or be reduced to zero over a short distance. The border arrangementin accordance with the present invention provides for such desiredcurrent roll off while providing uniform current distribution over theelectrode from border to border.

In addition, the present invention provides for indicia, which isprinted on the conductive flexible member in the border region and notcontacting the conductive ink pattern, for conveying written informationto a user. The indicia when disposed in the border do not affect currentdistribution or current “roll off” at electrode edges. Visualobservation of the indicia is enhanced through the utilization of aconductive hydrogel adhesive with sufficient transparency to enable theuser to read the indicia therethrough.

In yet another embodiment of the present invention, the medicalelectrode includes a moderately conductive flexible member having a topand a bottom side with a plurality of connectors in contact with theconductive member top side for establishing electrical contact withexternal apparatus, and a plurality of highly conductive patterns aredisposed on the conductive flexible member bottom side where eachelectrode is electrically isolated from an adjacent electrode.

This feature provides for the advantage of fixed electrode distanceswhich assures proper application of the electrode for optimum patientstimulation or signal recording when multiple electrodes are utilized.

A moderately high conductive adhesive is disposed on the conductivemember bottom side and covers the conductive ink patterns for adheringthe electrode to a patient's skin.

It should be appreciated that the lead wire may be attached or held inplace on the conductive flexible member top side in any manner, andinasmuch as the current distribution across the electrode conductive gelis controlled by the relative conductivities of the flexible member, inkpattern and the adhesive, the connector can be placed anywhere withinthe borders of the ink pattern as hereinabove noted.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood with reference to thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is an exploded cross-sectional view of a medical electrode inaccordance with the present invention generally showing a moderatelyconductive flexible member having a top side and a bottom side, aconnector in contact with the member top side, and a non-conductiveflexible sheet covering the moderately conductive flexible member topside and the connector, the sheet having dimensions greater than theflexible member; a highly conductive pattern is disposed on the memberbottom side, along with a moderately high conductive adhesive and aplastic carrier with a release layer, the carrier preventing prematureand/or inadvertent contact with the hydrogel;

FIGS. 2 a and 2 b are plan views of two embodiments of the presentinvention showing different ink patterns and indicia for identifying theelectrodes;

FIG. 3 is a plan view of yet another embodiment of the present inventionshowing several ink patterns disposed on a single conductive flexiblemember and a non-conductive flexible sheet extending beyond a perimeterof the member;

FIG. 4 is a plot of current distribution profile of the electrode shownin FIG. 1, (i.e. an electrode having a moderately conductive flexiblemember, a highly conductive pattern disposed on the member bottom sideand a moderately high conductive adhesive);

FIG. 5 is a plot similar to FIG. 4, and included for comparisonpurposes, of the current distribution of an electrode having amoderately conductive flexible member, a highly conductive patterndisposed on the member bottom side and moderately conductive adhesive;and

FIG. 6 is a plot similar to FIG. 5, and included for comparisonpurposes, of the current distribution of an electrode with no highlyconductive pattern disposed on a moderately conductive member bottomside, a moderately conductive adhesive and a connector disposed on a topside of the moderately conductive member.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, there is shown, in explodedcross-section, a medical electrode 10 in accordance with the presentinvention, which generally includes a moderately conductive flexiblemember 12 having a top side 14 and a bottom side 16.

A connector 20, which may include a lead wire 22 and jack 24 is providedwith the lead wire 22 in contact with the member top side 14.

A non-conductive flexible oversize sheet 26 covers the conductiveflexible member 12 along with the connector 20 in order to preventinadvertent contact with the conductive member 12 and connector 20. Thesheet 26 may be adhered to the flexible member 12 with any suitableadhesive 28 and also holds the lead wire 22 in contact with the member12. The sheet 26 has dimensions greater than overall dimensions of themember 12 resulting in an edge, or perimeter, 26 a which overlaps themember 12, see also FIG. 3. This structure eliminates the need foralignment of the sheet 26 with the member along their peripheries. Theadhesive 28 covers the entire sheet 26 include the edge 26 a. Thisenables the electrode 10 to be sealed along the perimeter 26 a to auser's skin (not shown). This, in turn, enables bathing or showering bythe user without degradation of the electrode/skin coupling. Water isprevented from entering the electrode 10 under the sheet 26.

The lead wire 22 may be of any inexpensive suitable conductive material.

The sheet 12 may be formed from any suitable carbon loaded elastomericfilm having suitable surface resistivity of between about 102 ohm/squareand about 106 ohm/square, for example, about 5000 ohm/square and atransverse resistivity of between about 103 and about 105 ohm/square,for example, about 104 ohm/square. Suitable polycarbonate polyolefin anda conductive ink pattern 30 may be printed, or otherwise transferred tothe conductive member bottom side 16 with various patterns 32, 34 forembodiments 36, 38, as shown in FIGS. 2 a and 2 b. The ink pattern mayhave a resistivity of between about 0.1 and about 10 ohm/cm.

With reference again to FIG. 1, the conductive ink pattern 30 contacts aconductive hydrogel adhesive 44, which is utilized for adhering theelectrode 10 to a patient's skin, not shown. The conductive hydrogeladhesive is formulated with moderately high conductivity for example avolume resistivity between about 102 and about 104 ohm cm, preferablyabout 400 ohm cm. Suitable gels are described in U.S. Pat. No.6,038,464.

A plastic, paper, or other suitable carrier 48 along with a releasecoating 50 may be provided in order to prevent inadvertent and/orpremature adhesion of the patients' skin or other object to thehydrogel. The plastic carrier 48 and release coating 50 is removed priorto application of the electrode 10 to the patients' skin.

Shown in FIG. 3 is another electrode embodiment 54 which includes amoderately conductive flexible member 56 having a plurality of highlyconductive ink patterns 60, 62, 64 disposed on a bottom side 62 of theconductive member 56. The conductive ink patterns 60, 62 and 64 may beof various shapes and grid patterns in order to customize the electricalconductivity of the electrode 54 beneath the pattern 60, 62, 64. Theadhesive, not shown in FIG. 3, is of moderately high conductivity ashereinabove described.

The spaced apart pattern 60, 62 and 64 act as separate electrodes andcommunicate with lead wires 72, 74, 76 respectively, which are attachedto a top side (not shown in FIG. 3) of the conductive member 56 asillustrated in FIG. 1 with the description of the electrode embodiment10.

The advantage of utilizing a common conductive member 56 with spacedapart ink patterns 60, 62, 64 is that this structure provides uniformityof spacing between the independent electrodes. This in effect provides atemplate to insure proper electrode placement on a patient's skin.

It should be appreciated that, as shown in FIG. 3, the connector 72, 74,76 are in placed over the ink patterns 60, 62, 64. The lead wires 72,74, 76 can be placed anywhere between the borders 80, 82, 84 of the inkpatterns 60, 62, 64 since the current distribution across the electrodegel 44 is independently controlled as hereinabove noted.

Referring again to FIGS. 2 a and 2 b, indicia, which may or may not beconductive ink, may be printed on borders 96, 98 and do not interferewith the current density of the electrode 10 if no contact is made withthe patterns 32, 34. The borders 96, 98 are created when the conductiveink patterns 32, 34 are disposed on the flexible member bottom side 16at a spaced apart distance from a perimeter 102, 104 of the conductivemember 12. That is, a perimeter 106, 108 of the ink patterns 32, 34 isspaced apart from the perimeters 102, 104.

FIG. 4 shows the current distribution profile for the electrodes shownin FIG. 2 utilizing a flexible conductive member having a surfaceresistivity of about 200 ohm/square, a conductive ink pattern havingconductivity of about 1 ohm/cm and a hydrogel such as set forth in U.S.Pat. No. 6,038,464 with a volume resistivity of about 400 ohm cm. Thispatent is incorporated by this reference thereto in its entirety fordescribing this type of gel in general electrical configuration whichmay be used to advantage in accordance with the present invention.

As shown in FIG. 4, the conductivity of a 2-inch (50 mm) squareelectrode is very uniform over almost the entire electrode surface withvery little edge effects, i.e. perimeter edges in which non-uniformconductivity occurs, typical with prior art electrodes. In FIG. 4, acenter area 110 represents high current density or current transfer bythe electrode, the peripheral area 112 represents low or no currentdensity and an intermediate area 114 represents a sharp roll off ofcurrent density. Because of the rapid roll off in current density, theefficiency of the electrode is enhanced since most of the electrode isutilized for providing uniform current density without burning edgeeffects.

The current density plot of FIG. 4 shows a vastly improved currentdensity over the electrode in FIG. 5 which is identical except for theuse of a moderately conductive adhesive (about 1100 ohm cm) instead of amoderately high conductive adhesive (about 400 ohm cm).

It should be clear that the current density shown in FIG. 5 isconsiderably more non-uniform than the current density shown in FIG. 4.Accordingly, the electrode efficiency in coupling current to a patent(not shown) is severly diminished.

FIG. 6 is a plot of current density of an electrode as constructedsimilar to the electrode of FIG. 5 with a moderately conductive flexiblemember and a moderately conductive adhesive but with the lead wiredisposed on top of the flexible member and no conductive pattern on thebottom side. The current density shown in FIG. 6 (which isrepresentative of prior art electrodes) is by far inferior to thecurrent densities shown in FIGS. 4 and 5 and illustrates that the uniquecombination of elements collectively provides an electrode havingunexpectedly improved current density.

The difference in conductivity or resistivity between the sheet 12 andthe lines 30 as well as the adhesive 44 enables precise control ofcurrent distribution which cannot be achieved, for example, with anon-conductive sheet or a highly conductive sheet. The conductivity ofthe adhesive is selected to be moderately high in order to enable thelead wire 20 to be disposed on top of the sheet 12 instead of in contactwith the pattern as with prior art electrode. This effect of adhesiveconductivity was heretofore not known and is an unexpected result. Inaddition, the ink pattern may be of varied conductivity in order totailor the current through the conductive sheet which may have athickness of up to about 10 mils, for example, about 1 mil.

Although there has been hereinabove described a specific reversecurrent-controlling electrode in accordance with the present inventionfor the purpose of illustrating the manner in which the invention may beused to advantage, it should be appreciated that the invention is notlimited thereto. That is, the present invention may suitably comprise,consist of, or consist essentially of the recited elements. Further, theinvention illustratively disclosed herein suitably may be practiced inthe absence of any element which is not specifically disclosed herein.Accordingly, any and all modifications, variations or equivalentarrangements which may occur to those skilled in the art, should beconsidered to be within the scope of the present invention as defined inthe appended claims.

1. A medical electrode comprising: a conductive flexible member having atop side and a bottom side; a connector in contact with the conductiveflexible member top side, for establishing electrical contact with anexternal apparatus; a non-conductive flexible sheet disposed over theconnector on the conductive flexible member top side, saidnon-conductive flexible sheet having dimensions greater than saidconductive flexible member causing an overlap thereof by a sheetperimeter; an adhesive for bonding said non-conductive flexible sheet tothe top side of said conductive flexible member and securing saidconnector to said conductive flexible member top side; a conductivepattern disposed on the conductive flexible member bottom side; and aconductive adhesive disposed on the conductive flexible member bottomside and covering said conductive pattern, for adhering the electrode toa patient's skin.
 2. The electrode according to claim 1 wherein saidconnector is disposed over said conductive pattern.
 3. The electrodeaccording to claim 2, wherein said conductive pattern is disposed on theconductive flexible member bottom side at a spaced apart distance from aperimeter of said conductive flexible member to establish a borderbetween a perimeter of said conductive pattern and the conductiveflexible member perimeter for providing controlled roll off ofelectrical current distribution of the electrode.
 4. The electrodeaccording to claim 1 wherein said adhesive is disposed over the entireflexible sheet including the sheet perimeter, the adhesive in the sheetperimeter enabling sealing of the electrode to a user's skin.
 5. Amedical electrode comprising: a conductive flexible member having a topside and a bottom side; a plurality of connectors in contact with theconductive flexible member top side, for establishing electrical contactwith an external apparatus; a non-conductive flexible sheet disposedover the connector on the conductive flexible member top side, saidnon-conductive flexible sheet having dimensions greater than saidconductive flexible member causing an overlap thereof by a sheetperimeter; an adhesive for bonding said non-conductive flexible sheet tothe top side of said conductive flexible member and securing saidconnector to said conductive flexible member top side; a plurality ofconductive patterns disposed on the conductive flexible member bottomside; and a conductive adhesive disposed on the conductive flexiblemember bottom side and covering said conductive patterns, for adheringthe electrode to a patient's skin.
 6. The electrode according to claim 5wherein one of said plurality of connectors is disposed over acorresponding conductive pattern.
 7. The electrode according to claim 5,wherein each of said conductive patterns are disposed on the conductiveflexible member bottom side at a spaced apart distance from a perimeterof said conductive flexible member to establish a border between aperimeter of each of said conductive patterns and the conductiveflexible member perimeter for providing controlled roll off ofelectrical distribution of the electrode.
 8. The electrode according toclaim 5, wherein said adhesive is disposed over the entire flexiblesheet including the sheet perimeter, the adhesive in the sheet perimeterenabling sealing of the electrode to a user's skin.